2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Modeling: CAD, Scan Patterns, Contouring, Slicing I
Program Organizers: Joseph Beaman, University of Texas at Austin
Monday 1:30 PM
August 14, 2023
Room: Salon A
Location: Hilton Austin
Session Chair: Nicholas Meisel, Pennsylvania State University
1:30 PM
Single Path Generation for Closed Contours via Graph Theory and Topological Hierarchy: Michael Borish1; Alex Roschli1; Charles Wade2; Brian Post1; Liam White1; Cameron Adkins1; 1Oak Ridge National Laboratory; 2University of Colorado Boulder
Slicing converts a 3D object into a set of 2D polygons that are filled with multiple path types. These paths involve travels where the extruder of the machine must stop building, lift, travel to the next path, lower, and resume construction. Travels are considered wasted time as construction of the object is not occurring. Further, the start/stop point, called a seam, causes both reduced aesthetic and weaker material properties. To address these issues, an algorithmic approach was developed to compute a continuous single path from closed contours. The algorithm utilizes graph theory and a topological hierarchy to produce a single path for an individual layer. This approach can be combined with spiralization techniques to compute a single path for entire objects. The resulting objects can be constructed quicker and have improved material properties as verified via tensile testing.
1:50 PM
Path Planning for Non-Planar Robotic Additive Manufacturing: Michael Geuy1; Jay Martin1; Timothy Simpson1; Nicholas Meisel1; 1Pennsylvania State University
As material extrusion additive manufacturing continues to mature, there is increasing need for an extrusion path planning (“slicing”) method that takes advantage of the capabilities of many-degree-of-freedom systems like those used in Robotic Material Extrusion (RoMEX). In this paper, key principles from planar, multi-planar, active-Z, and conical slicing techniques including variable layer thickness, nozzle angle control, and arbitrary layer shape have been integrated into a novel strategy. Specifically, 3D surfaces are used as the basis of non-planar layer generation without the need to decompose the object into regions. This surface is used as a layer parting line and is stacked along a single axis to produce non-planar layers that leverage the kinematics of a RoMEX system. This approach is capable of quickly producing parts with complex geometries, quality surface finish, and improved mechanical properties by leveraging layer shapes that are self-supporting with high interlayer bonding.
2:10 PM
Novel Concepts to Integrate Dense and Sparse Infill Regions in Material Extrusion AM Parts: Logan Hutton1; Joseph Bartolai1; 1Pennsylvania State University
Modern toolpath generation softwares, or “slicers," allow for multiple regions within a Material Extrusion Additive Manufacturing produced part to be assigned different processing parameters, including infill density. Contemporary slicers develop these different infill regions independently, leading to discontinuities in the toolpaths at the region's boundaries. This work investigates the effect these discontinuities have on part strength, and tests a variety of novel approaches to connect infill regions in a continuous manner to improve part properties. Mechanical properties of parts built by toolpaths generated using Ultimaker Cura and Slic3r are compared to those of parts built using the novel build strategies presented in this work. The continuous and sequential novel build strategies presented in this work show statistically significant mechanical property increases.
2:30 PM
Modeling and Correcting Illumination Inhomogeneity over Multiple DLP Illumination Intensities for Better Fabrication Accuracy: Saroj Subedi1; Henry Oliver Ware1; 1North Carolina State University
Within custom Digital Light Processing (DLP) systems, various small issues either in the optical assembly or with the DMD can lead to non-uniform illumination at the curing interface. This inhomogeneity leads to inaccurate dimensions of fabricated features over the full print area. To remedy this in our system, we have explored the relationship between LED output illumination, broke the illuminated area into a regional mesh, measured the light intensity and grayscale values over the mesh to obtain region-specific grayscale mask adjustments for illumination-leveling. This process involves producing grayscale mask by quantifiably balancing the light intensity values over build area and thus obtaining more uniform printed features. We compared the dimensional accuracy of features printed using full white pixel value images for 250µm features and those obtained using illumination-leveling grayscale processed images. Our results demonstrate the effectiveness of our method to obtain dimensionally accurate features, thanks to the achieved uniform illumination.
2:50 PM
Voxel-free Radon Transform for Improving Surface Quality in Computed Axial Lithography: Jennings Ye1; Yaxuan Sun1; Hayden Taylor1; 1University of California, Berkeley
Computed axial lithography (CAL) is an additive manufacturing process that projects light patterns into a rotating volume of photosensitive resin to print the desired object through the superposition of light energy. Currently, these projection patterns are generated by voxelizing a target object from an STL or another 3D file format and applying the Radon transform followed by an iterative optimization process. This work proposes a voxel-free method to transform the target object into the projection space. Here, the Radon transform is performed directly on a non-voxelized target object by finding intersections between incident rays of light and triangles of the original STL surface mesh. Initial simulated results show a more consistent dose gradient at the edges of the printed object, indicating improved surface quality and smoothness. Additionally, simulations show a more uniform object interior using the proposed method.
3:10 PM Break
3:40 PM
Level Set Grids for Hybrid Manufacturing: Liam White1; Bryan Quaife2; Michael Borish1; Cameron Adkins1; Alex Roschli1; 1Oak Ridge National Laboratory; 2Florida State University
To ensure optimal part quality, accurate model representation is essential. Traditional additive manufacturing methods utilize STL meshes, which often lack precise curvature information. This information is critical for hybrid or post-manufacturing subtractive processes. When alternative mesh representations are unavailable, such as in object repair scenarios, curvature information must be derived from a triangulated mesh. To address this, an innovative approach employing sparse volumetric grids to voxelize a mesh’s volume was developed. Utilizing this representation, calculating the gradient of the level set function within the grid yields accurate curvature information where none previously existed. Leveraging this information, surface pathing can adhere to the object's curvature enabling accurate pathing for hybrid and subtractive processes. Furthermore, a partial object representation is possible that facilitates synchronous additive and subtractive processes.
4:00 PM Cancelled
Developing an Application Programming Interface for Hypocycloid-based Inner and Outer Gears of Progressive Cavity Pumps in Advanced Extrusion Applications: Yusuf Furkan Ugurluoglu1; Piergiorgio Gentile1; Ana Ferreira-Duarte1; Javier Munguia2; 1Newcastle Unviersity; 2Warwick University
Additive manufacturing has transformed the field of bioprinting, enabling the creation of complex tissue structures with exceptional precision. Recently, there has been interest in using progressive cavity pumps (PCPs) as an advanced extrusion method in bioprinting applications. Some studies have shown that PCPs offer better accuracy than the traditional method of syringe-based extruders. However, PCPs were originally designed for the adhesive dispensing industry and need to be adapted for bioprinting applications. To address this issue, an application programming interface (API) was developed in this study to model the intricate components of the inner and outer gears of PCPs. A hypocycloid-based API was presented in this research with the adjustable parameters of the number of outer gear lobes, generator radius, tolerance, cusp diameter, number of gear turns and gear height. This API will be a valuable tool for supporting PCP research in academia and designing PCPs for specific bioprinting applications.
4:20 PM Cancelled
Computer Modelling of Residual Stress Development During Selective Laser Melting of 17-4 PH Stainless Steel and Experimental Validation via Contour Method: Yusuf Polat1; 1Yunus Emre
SLM is a promising manufacturing technique which has been developed significantly in recent years. Additive nature of the process enables manufacturing of complex geometries with minimum wastage. However, residual stress formation during building of SLM process has negative effects on mechanical properties and service life such as cracking or reducing fatigue life therefore strong understanding of residual stress is required in order to mitigate the detrimental effects. At this point numerical simulation techniques offer an applicable practice for the understanding, prediction and mitigation of residual stress problem. In this study, macro scale mechanical and thermomechanical simulations are practiced with Simufact Additive software for SLM processing. Experimental validations are practiced with contour method. Experimental and computational efforts yielded highly consistent results. The applicability of the Contour method in bulk SLM parts has been confirmed and the simufact additive software has been verified to give reliable results as a simulation tool.